The invention relates generally to fixation of cut and rotated bone portions following a proximal, tibial osteotomy. More particularly, the invention concerns a fixation plate and fasteners for use in fixing the proximal tibial and metaphyseal tibial portions as a final step in performing a tibial plateau-leveling curvilinear-cut and rotate osteotomy.
A proximal tibial osteotomy for leveling a canine's tibial plateau involves producing in the proximal tibia a curvilinear through cut that separates the metaphysis from the proximal tibia, rotating the metaphysis relative to the proximal tibia a predetermined amount that effectively levels the tibial plateau and fixing the metaphysis relative to the proximal tibia by suitable means. Such an osteotomy is described in detail in my U.S. Pat. No. 4,677,973 entitled "Proximal, Tibial Osteotomy for Leveling A Tibial Plateau", which issued Jul. 7, 1987, the disclosure of which is incorporated herein by this reference. While the osteotomy method disclosed therein is effective in leveling the tibial plateau, fixation as by pinning and/or wiring is not always as effective as desired in the short and long-term fixation of the cut and separated, and relatively rotated, tibial portions. Less secure fixation can result in retarded osteosynthesis and, ultimately, failure of the proximal tibia and/or the femoro-tibial joint.
Accordingly, it is a principal object of the present invention to provide a fixation plate and fasteners for use in fixing the relatively rotated bone segments that result from a tibial plateau-leveling osteotomy.
Another object is to provide such a plate that accommodates a wide range of choice in compressively, distractively or neutrally impacting the bone segments in their fixation relative to one another.
Yet another object is to provide such a plate the formed screw holes of which maximally conform along at least one axis, to fasteners used in securing the plate to the osteotomy site.
Another important object of the invention is to provide such a plate that generally conforms in three dimensions to the proximal tibia for which it is particularly suited.
Still another object is to provide such a plate with a plural screw hole configuration that, with fasteners properly inserted therethrough into the bone segments, provides for better securement of the plate to the proximal tibial site due to cooperation among certain of the hole/fastener pairs.
It is also an object of the invention to provide such a fixation plate and fastener set that easily and cost-effectively are manufactured.
In brief summary of the invention, an elongate tibial plateau-leveling osteotomy fixation plate is provided that in cross-sectional view along its long axis is curved to conform along its extent with the differently cross-sectionally curved proximal tibial segment and metaphysis. The plate is shaped and dimensioned in its generally sagittal planar extents to conform in part with the elongate proximal tibia, with a generally triangular, cranially extending expanse at its proximal end. The plate preferably has formed therein six holes, three triangularly arrayed in the triangular proximal expanse overlying the metaphysis and three linearly arrayed in the elongate distal expanse overlying the proximal tibia (with the preferably cylindrical osteotomy cut, separated, relatively rotated and conformingly mating surfaces extending between these sets of holes).
Preferably two of the holes in the triangular expanse are elongate, with their long axes intersecting at the center of the curvilinear osteotomy. The two elongate holes include in their circular ends oppositely 45.degree. beveled features that allow the plate, when secured by screws in all six holes, compressibly or distractably to urge the proximal tibia and the metaphysis together or apart along a radius of the osteotomy that generally bisects the arc of the curvilinear cut, or neutrally to fix them in a position of neither compression nor distraction. All six holes include in their remaining regions arcuately curved "countersink" beveled features that conform precisely with the curved head of the screws with which the plate is fixed to the osteotomy site. The compressive/distractive forces incident to securing one or more screws through the elongate hole(s) into the metaphysis cooperate with the forces incident to securing one or more screws through the round hole(s) into the proximal tibia, thereby better to fix the plate against inadvertent movement relative to either section.
These and other objects and advantages of the invention will be more clearly understood from a consideration of the accompanying drawings and the following description of the preferred embodiment.